The present invention relates to an electronic tone generating system and particularly to such a system for reproducing organ tones having improved harmonic content.
Electronic tone generation as employed in electronic organs typically simulates the musical sound produced by a pipe organ, within reasonable cost constraints placed on the instrument. Each note on each organ manual may be generated by an electronic oscillator the output of which is modified by stop-controlled wave shaping circuitry to resemble a pipe organ waveform. Divider chains can be utilized to reduce the number of oscillators necessary. Other organ systems include computer circuitry for calculating elemental samples of a complex musical waveform and/or storing the same in memory from which the samples are retrieved at a rate proportional to the frequency or pitch of the desired output.
At least in principle, individual tone generator circuits are not required for the generation of each complex organ output wave shape. Instead, oscillators could generate sine wave components for additive combination into complex waveforms. Unfortunately, the exact generation of all the harmonics for all the notes on an organ would require an impractically large number of individual sine wave generators. Heretofore, organ systems using this type of approach have relied for harmonic generation on the higher frequency note generators in the same musical scale as the selected fundamental. Thus, the second harmonic of any given note is the corresponding note in the next octave up the scale, the fourth harmonic is two octaves up, the eighth is three octaves up, etc., while close correspondence may also be found on the musical scale for other harmonics such as the third, fifth and sixth. However, reproduction is usually limited to the first few lower order harmonics because of the divergence between many of the higher harmonics and higher notes on the scale. A good reproduction of pipe organ tones, on the other hand, requires a much larger number of harmonics.